story: A440 or A4 (also known as the Stuttgart pitch), which has a frequency of 440 Hz, is the musical note of A above middle C and serves as a general tuning standard for musical pitch. 
  
  The International Organization for Standardization classify it as ISO 16. Prior to the standardization on 440 Hz, other frequencies were standardised upon. Although not universally accepted, it serves as the audio frequency reference for the calibration of acoustic equipment and the tuning of pianos, violins, and other musical instruments. 
  
  Prior to the standardization on 440 Hz, many countries and organizations followed the French standard since the 1860s of 435 Hz, which had also been the Austrian government's 1885 recommendation. Johann Heinrich Scheibler recommended A440 as a standard in 1834 after inventing the "tonometer" to measure pitch, and it was approved by the the same year. 
  
  The American music industry reached an informal standard of 440 Hz in 1926, and some began using it in instrument manufacturing. In 1936 the American Standards Association recommended that the A above middle C be tuned to 440 Hz. This standard was taken up by the International Organization for Standardization in 1955 (reaffirmed by them in 1975) as ISO 16. Although not universally accepted, since then it has served as the audio frequency reference for the calibration of acoustic equipment and the tuning of pianos, violins, and other musical instruments.
questions: What entity standardized A4 on 440 Hertz?
questions: What do they classify it as?
questions: Was A4 always standardized at 440 Hertz?
questions: What is one instrument A4 is used to tune?
questions: And another?
questions: Do they mention tuning guitars?
questions: What is A4 also called?
questions: Or what else?
questions: What note is it?
questions: In the 1920s, did the American music companies have A4 as an official standard?
questions: Who made a recommendation in 1936?
questions: What did they recommend?
questions: What happened in 1955?
questions: When did they reiterate their support for A4?
questions: Does everyone agree with the standard?
questions: What did Scheibler invent?
questions: What did it do?
questions: When did he create it?
questions: How many Hertz was the French standard?
questions: Since when?
answers: International Organization for Standardization
answers: This standard was taken up by the International Organization for Standardization in 195
answers: ISO 16
answers: This standard was taken up by the International Organization for Standardization in 1955 (reaffirmed by them in 1975) as ISO 16
answers: no
answers: Prior to the standardization on 440 Hz, other frequencies were standardised upon
answers: pianos
answers: it serves as the audio frequency reference for the calibration of acoustic equipment and the tuning of pianos, violins, and other musical instruments. 
answers: violins
answers: calibration of acoustic equipment and the tuning of pianos, violins, and other musical instruments. 
answers: no
answers: n. Although not universally accepted, it serves as the audio frequency reference for the calibration of acoustic equipment and the tuning of pianos, violins, and other musical instruments. 
answers: A440
answers: A440 or A4 (also known as the Stuttgart pitch),
answers: Stuttgart pitch
answers: A440 or A4 (also known as the Stuttgart pitch
answers: A above middle C
answers: is the musical note of A above middle C
answers: no
answers: The American music industry reached an informal standard of 440 Hz in 1926, 
answers: the American Standards Association
answers: In 1936 the American Standards Association recommended
answers: that the A above middle C be tuned to 440 Hz.
answers: that the A above middle C be tuned to 440 Hz.
answers: it was used by the International Organization for Standardization in 1955
answers: his standard was taken up by the International Organization for Standardization in 1955 
answers: 1975
answers: (reaffirmed by them in 1975)
answers: . no
answers: . Although not universally accepted, since then 
answers: the tonometer
answers: ohann Heinrich Scheibler recommended A440 as a standard in 1834 after inventing the "tonometer" to measure pitch, and it was approved by the the same year.
answers: measure pitch,
answers: the "tonometer" to measure pitch,
answers: 1834
answers: d in 1834 after inventing the "tonometer" to measure pitch, and it was approved by the the same ye
answers: 435 Hz, w
answers:  the French standard since the 1860s of 435 Hz, w
answers: 1860
answers: the French standard since the 1860s of 435 Hz